Resin to the Rescue

For some insertions, steam was introduced to bring the resin to its cure temperature

Collierville, Tenn., has a quaint downtown district with a classic gazebo town square that is listed on the National Register of Historic Places. When the city’s underground sewer pipelines began showing signs of weakness, officials knew tearing up streets to replace the pipe would have been a civic nightmare.

The trenchless solution designed by consulting engineers Jordan, Jones & Goulding, Inc. (JJG) had new seamless cured-in-place-pipe (CIPP) built inside the old pipe. Insituform Technologies, Inc. (ITI) installed the CIPP using a felt tube saturated with Vipel corrosion-resistant resin made by AOC. Adding a dimension of community pride to the project, AOC’s world headquarters is about five minutes away from downtown Collierville.

“If this project had been standard open-cut construction, it would have taken six months instead of the four-and-a-half weeks it took,” said Insituform’s Senior Project Engineer Randy Hansbrough. “By not having to dig trenches, the environment and town ambiance were preserved. Businesses did not have to face shutdowns, and roads stayed open to traffic.”

The Collierville project rehabilitated 12,800 ft of 8 in. of vitrified clay and concrete sanitary sewer pipe installed in various stages in the 1960s.

“This was a major infrastructure management undertaking,” said Murray Beard, project manager for the Collierville Public Service Department. “There were a variety of issues in different areas. In some places, soil settlement was causing depressions in the roadway. There were leaking joints, root intrusions were causing backup, and we had inflow and infiltration of storm waters during heavy rains.”

Making old pipes new

Steve Lindsey, senior pipelines rehabilitation specialist for JJG, developed the solution by having the host pipe cleaned out and then relined with CIPP.

The process started with a nonwoven, polyester felt liner custom made for the host pipe and in predetermined lengths for onsite insertions. Prior to insertion, the felt was impregnated with wet resin, then was shipped to the jobsite under controlled conditions to prevent premature resin cure.

To speed up installation, minimize disruption and eliminate digging, access to the Collierville sewer pipe was achieved through existing manholes. As the wet-out tube was inserted, internal water pressure or air pressure was used to invert the tube and move it forward against the pipe’s inner wall. Depending on the pipe conditions and location for a specific inversion, either the water was heated or steam was introduced to raise the temperature of the resin to its curing point. Temperature was then maintained for a specific time to ensure a complete cure. When fully cured, the resin became a cross-linked solid, resulting in a new seamless liner inside the old pipe.

The Vipel resin for the job was a high molecular weight, isophthalic polyester engineered for CIPP use and proven in applications throughout North America. Lindsey pointed out the significance of CIPP resin specification saying, “As important as the felt tube is, it is just the vehicle for getting the resin inside the host pipe. The resin is the new pipe.”

“Collierville shares a common thread with many other small towns we’ve been to across America,” said Bill Crockett, field engineer for ITI. “Their sewer infrastructure was aging, and digging up Main Street would be incredibly disruptive.”